
Empirical Investigation ◾ 163
e lines in Figure 4.8 are parallel, which indicates that the two vari-
ables have no eect on each other. us, an individual line shows the main
eect of the variable it represents. In this case, each line shows that the
time to code a module increases with the size of the module. In comparing
the two lines, we see that reuse reduces the time to code a module, but the
parallel lines indicate that size and degree of reuse do not change the over-
all trend. However, if the results resemble Figure 4.9, then there is indeed
an interaction between the variables, since the lines are not parallel. Such
a graph ma